1. Field of the Invention
The present invention relates to a silicon substrate processing method for forming a penetrated hole on a silicon substrate and a method of manufacturing a liquid discharge head that discharges a liquid such as an ink onto a recording medium such as a recording sheet.
2. Description of the Related Art
As a liquid discharge head that discharges ink in the form of liquid, a type of liquid discharge head that discharges ink upwardly with respect to the heater that generates discharge energy is known. (This type of head will be hereinafter referred to as the side shooter type head.) This side shooter type head has a configuration in which a penetrated hole is provided in a silicon substrate on which heaters are formed and ink is supplied from the back side opposite to the surface on which the heaters are formed, through an elongated ink supply port in the form of a penetrated hole.
In the side shooter type head, the ink supply port that penetrates the silicon substrate may be formed, for example, by the method disclosed in U.S. Pat. No. 6,139,761. U.S. Pat. No. 6,139,761 teaches to form an ink supply port on a silicon substrate having a <100> surface of the orientation of crystal plane by anisotropic etching using a strong alkaline solution. In this anisotropic etching of the silicon substrate, the ink supply port is formed utilizing a difference in the solubility of the silicon substrate to the strong alkaline solution between the surface of a crystal plane orientation of <100> and the surface of a crystal plane orientation of <111>.
In the process of forming an ink supply port in a silicon substrate by anisotropic etching using a strong alkaline solution, etching process takes a relatively long time, which is one of the factors that deteriorate the efficiency of production of liquid discharge heads.
In addition, as shown in FIG. 4, the ink supply port 106 formed by anisotropic etching has a tapered cross-sectional shape in which the opening sectional area gradually decreases from the back surface toward the front surface at the angle of 54.7° formed by the <111> surface. In other words, the opening width of the ink supply port 106 on the back surface of the silicon substrate 101 is larger than the opening width of the ink supply port 106 on the front surface of the silicon substrate 101 on which heaters 103 are provided. Consequently, the lateral width (or the shorter side dimension of the elongated ink supply port) of the device substrate (i.e. the substrate for liquid discharge head) that constitutes a liquid discharge head having heaters and nozzles for discharging ink depends on the opening width of the ink supply port on the back surface of the silicon substrate. Thus, the largeness of the lateral width of the inkjet chip leads to an increase in the manufacturing cost of the liquid discharge head. Therefore, in order to reduce the manufacturing cost, it is necessary to make the opening width of the ink supply port on the back surface of the inkjet chip smaller thereby reducing the lateral width of the inkjet chip.
To achieve this, there has been developed a method in which an ink supply port having walls that are perpendicular to the front and back surfaces (principal surfaces) of a silicon substrate is formed by dry etching. Furthermore, for example U.S. Pat. No. 6,648,454 discloses a method in which dry etching and anisotropic etching are performed in combination to form walls of an ink supply port that are perpendicular to the front and back surfaces of a silicon substrate.
However, in cases where dry etching is used in the process of forming an ink supply port as described above, the etching process takes a relatively long time. Therefore, it is demanded to reduce the etching time to improve the production efficiency.